Method and apparatus for detecting fluid movement in well bores



ocg. 13, 1953 J. E. wALs'rRoM 2 655 631 METHOD AND APPARATUS FOR DETECTING FLUID MOVEMENT IN NELL BORES Filed April 28, 1951 INVENTOR JOHN E. WLSTROM Patented Oct. 1,3, 1953 METHOD AND APPARATUS FOR DETECTING FLUID MOVEMENT IN WELL BORES John E. Walstrom, Danville, Calif., assignor vto California Research Corporation, San Francisco, Calif., a corporation of Delaware Application April 28, 1951, Serial No. 223,516

9 Claims.

The present invention relates to method and apparatus for detecting the movementof' fluids in a. well bore, and more particularly relates to method and apparatus for determining the direction of fluid flow in a well bore, whether said flow is due to the entrance of contaminating fluids into the well or due to the loss of Well fluid to an earth formation through which the well bore passes.

Heretofore, in the art of detecting the influx or `ingress of contaminating fluids or water drive fluid into a Well bore, such as the entrance of water into a producing oil well at an unknown level, it has been common practice to provide a pair of electrodes in the well bore with at least one' electrode at the level to be investigated. The electrical resistance between that pair of electrodes is then measured by the application of an external current source of either A. C. or D. C. potential. Changes in the electrical resistance are then correlated with the depth of the electrodes to locate the elevation at which water is entering the well. In some instances it has been proposed that the fluid in the well be entirely replaced by a test solution prior to making these resistance measurements. Another method proposed in the prior art is that of introducing an electrolyte solution into the well to create a volatic cell between a pair of electrodes of dissimilar materials to generate a potential. Movement of well fluid may then displace the electrolyte to vary the potential measured between the electrodes and the direction of movement of fluid determined by such variations in potential.

While the foregoing apparatus and methods A The present inventionrelates to an improved method and apparatus for detectingmovement of well fluids disclosed in the copending application of Gilson H. Rohrback, Robert A. Stoner,

Malcolm Macaulay and William T. Cardwell, Jr.,

Serial No. 211,304, filed lFebruary y16, 1951, for Method and Apparatus for Detecting Fluid Movement in a Well Bore, now Patent No. 2,596,437.

It is an object of the invention to provide an apparatus for detecting the location in a well where fluid is entering or leaving the Well by v measurement of fluid movement without interference by the natural or self-potentials existing in the well bore.

between a pair of electrodes positioned in the well have been fairly satisfactory in detecting water ingress into a producing oil well, each of these systems requires either the application of an external source of current or the introduction of modifying fluids into the well bore. Accordingly each requires the use of quite complex equipment in the well bore. Additionally, apparatus constructed in accordance with the prior art has not been directly applicable to the problem of detecting the level at which drilling fluid is lost during the drilling of oil wells by conventional rotary methods. One satisfactory type of apparatus which has been useful in locating the position in a well bore Where fluid is being lost is disclosed in the copending application of Marshall B. Standing, Harry S. Yaplee and Malcolm Macaulay, which issued as Patent No. 2,581,979. However, this apparatus requires means for introducing an electrolyte fluid capable of changing the resistance characteristics of the drilling fluid.

bore when one of the electrodes is directly in physical contact with the moving fluid stream and the other electrode isA only in electrical or ionic contact with said stream and correlating the movement of fluid with the elevation or depth of the electrode pair in the well bore.

Further objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing which forms an integral part of the specification.

In the drawing:

Fig. 1 is a cross-sectional elevation view of a down hole test instrument constructed in accordance with the present invention.

Fig. 2 is a plan view in the direction of arrows 2-2 in Fig. 1, showing the upper end of the down hole test instrument.

Fig. 3 is a partial cross-sectional view of ap-\ is preferably constructed ofelectrically conduc- 3 tive material, at any desired level in the well bore, end member i6 may be provided with a threaded flange portion I1 which has a bore I8 therein adapted to-receive an expanded end I8 of a conventional well-logging cable means 20. Cap nut 2| is adapted to engage the threads on flange I1 to secure together expanded portion I0 of cable 2l and end closure It.

As shown, the upper end of cable 20 desirably passes over a pulley member 22 at the earth's surface. Pulley 22 may be driven by any conventional means such as an electrical motor (not shown), and is preferably inter-connected to an elevation. or level, recording means 22.

As particularly illustrated in Fig. 1, a concentric insulating internal shield or shell 24 extending substantially the length of the casing or housing I and constructed of Bakelite, rubber or the like is so positioned that the external casing Il provides essentially a short-circuit electrical-conducting path for natural or self potentials existing in the well or bore hole due to dissimilar materials, including liquids and solids, present in the bore hole, and the adjacent earth strata traversed by the bore hole. In this way, fluid passing through the instrument may be made substantially free of potential modulations created by natural or self-potentials in the well. A pair of insulating bosses 25 and 26 are positioned at substantially the same elevation within shell or sleeve 24 and attached thereto so that a pair of metal eletcrodes 21 and 28 may be mounted within the insulated cylindrical passageway means provided by casing Ill and shield or sleeve 24. Electrodes 21 and 28 are preferably, but not necessarily, formed of the same material and are respectively connected to logging cable 20 by insulated leads 29 and 30. As illustrated, electrode 28 is preferably bare, although it may be provided with a conductive metal coating, while electrode 21 is provided with a porous or liquid-permeable-insulating covering or casing 3|. In the preferred arrangement, coating ll comprises a cotton batting surrounding the electrode and an overlying protective layer of linen tape. It will be apparent to those skilled in the art that the function of the porous layer surrounding electrode 21 is to permit the free interchange of ions between the surrounding liquid and the surface of metal electrode 21 through permeable-insulator-covering Il.

Electrode leadsV 29 and 30 are connected to surface potential indicating means through cable 20 and slip ring assembly 32, which may be con-' nected to potential or current-responsive means,

such as amplifier 33 and a recording millivolt meter 24. i

As best seen in Fig. 2, it will be noted that upper end member l is preferably provided with three openings or ports, designated generally as I5, adapted to permit well fluid to pass freely through the passageway provided through the interior of the test instrument. Lower closure member I8 is preferably open so that fluid may either enter or leave the interior of the test instrument through opening 38 provided in member I4.

Referring now to Fig. 3, wherein there is shown an arrangement particularly useful in connection with the determination of casing leaks or breaks. it will be noted that a rubber or flexible packing cup arrangement I1 is so formed that an upper portion 38 is adapted to grip or contact the outer surface of housing I0 while a radially outwardly extending portion 39 is arranged to slidably engage the inner surface 4|| of the well casing, liner or the like designated generally as 4|. The function of cup means I1 in this particular arrangement is to increase substantially the rate of flow of well fluid through the test instrument. It will be apparent that a similar cup arrangement may be provided adjacent the upper end of casing I0 adapted to force fluid to flow downwardly into the instrument through ports I5 in upper member Il. Likewise vthis arrangement may be used in unlined or uncased bore holes where there is a relatively uniform diameter in said well bore.

In operation, it will be apparent that housing may be lowered by means of cable 20 and pulley 22 into a well bore in which it is desired to detect the movement of fluid. If, as contemplated by the present invention, the apparatus is being used for detecting the location in a drilling well where fluid is being lost, the test will be conducted when circulation has been stopped, that is, when fluid is neither being added nor withdrawn from the well. Under these conditions there will be a displacement of normal well fluid due to the pressure differences existing between the formation and the well bore. Accordingly, in a drilling well, the well fluid will normally move downwardly from the top of the wall to the lower pressure formation to which fluid is being lost. At the same time, there will be virtually no movement of fluid in the bore below that level. On the other hand, when the apparatus is being operated to detect water entering a producing well or bore hole either through a leak or break in the casing or from a high pressure formation in an uncased portion of the well bore, the water so entering, being of greater specific gravity than the oil, may tend to migrate downwardly through the oil from the level at which the duid enters. Accordingly, in operation of the apparatus in detecting the location where fluid is either being lost during drilling or water is entering a producing well bore, the well fluid whose motion is to be detected will in general be downward. However, under some circumstances, upward flow may be encountered and it is not intended to limit the operation of the apparatus to a patricular direction of fluid movement.

In either operating function, electrode pair 21 and 2B are adapted to be in continuous electrical contact with the well fluid whose movement is tolbe detected. However, by virtue of the fact that electrode 28 is substantially bare, it is sub- .iected directly to the moving fluid while at the same time electrode 21 is substantially physically isolated from the movement of the fluid but remains in electrical or ionic contact therewith. Under these conditions, it has been found that a potential difference is created between the two electrodes by the movement of fluid over bare electrode 28. This potential is believed to be due to the removal of ions immediately surrounding a bare metal electrode and occurs when the fluid moving over such an electrode is at least partially conductive, i. e. contains electrically active ion species. Metals which have been found satisfactory for the establishment of this type of potential are zinc, brass, copper and silver, since these metals develop a substantially greater electrical potential than other similar metals under bore hole conditions. However, other metals may be used. Since the potentials developed between a pair of electrodes of this type are generally in the range of millivolts for a liquid velocity of a into or4 out of a wien bare. Addiuonany, the. present invention provides an apparatus for del f, tecting the movement of well fluids by measure- A ment of the potentials created by movementcf of the test instrument due to such natural or self-potential effects. Accordingly-the potential measured between electrodes 21 and'J 28 will be due substantially to velocity of fluid ilow alone, independent of the dissimilar materials surrounding the instrument. f

As noted in connection with the description of Fig. 3, cup member 31 may be provided to increase the velocity of flow through the instrument housing, especially when the instrument is utilized in locating influx of water.

With housing l positioned at a pre-determined level in the well bore, well fluids are allowed to pass through the passageway means by flowing in or out through ports 35 in upper member l5 and opening 36 in lower member i6. When fluid flows through the passageway means in the test instrument, a potential difference will be created between electrodes 21 and :28 by such movement of well fluids which may be detected by meter means 34 and recorded on chart drive apparatus 23. In detecting the loss of circulating drilling fluid to a low pressure formation, the detection of a potential difference between the electrodes will directly indicate that fluid is passing through the test instrument. The instrument may then be successively moved downwardly in the well bore and stopped at any desired interval until a position is obtained where the potential difference issubstantially reduced i l to zero. At this position there will be no downward movement of well fluid and in this way the low pressure or thief formation may be located and the depth of such formation identified by the recording means.

When the apparatus is being used to detect influx of water into a producing well, such inflowing fluid may be moving either upwardly or .downwardly in the well liner or casing, and in this instance such direction of fluid movement may be detected by moving the housing either upwardly or downwardly relative to an original, pre-determined position and then noting whether the potential difference increases or decreases when such movement of the housing is made. If the potential difference increases, it will be apparent that the direction of flow of the well fluid is opposite to the movement of the housing due to the increased velocity of fluid movement over electrode 28. On the other hand, if the potential decreases, the direction of fluid movement is in the same direction as the movement of the instrument. In this way the rate of flow may also be determined by moving the instrument at such a rate that the potential difference is substantially zero.

From the foregoing detailed description, it will be apparent that the present invention provides an improved method and apparatus for detecting fluid movement in a well bore without the necessity of introducing electrolyte solutions or externally energizing a set of test electrodes. This invention likewise provides an apparatus which is rugged and inexpensive to build and capable of detecting movement of fluid either surface from the bore hole. .l v L It will be apparent to those skilled in the'art f that numerous modifications and changes may` the well fluids AWithout interference from, nat-y v ural or self-potentials existing in the well boreand requiring a minimum ofy electrical cable/f' the earths leads for transmitting information to be made in the apparatus disclosed herein without departing from the teaching ofthis invention; Accordingly, all such modifications and changes as fall within the scope of the appended claims'are thereby intended to be included.

1. A method for `determining a characteristic of liquid ow comprising placing the surface of a rstelectrode in/ physical and electrical contact with a flowing liquid, placing a porousinsulator-covered second electrode in ionic contact with said liquid, shielding both of said `electrodes from electrical potentials resulting from the environment of the liquidand determining the potentialv difference between said electrodes,

as a measure of said rliquid flow characteristic. f

2. A method for determining liquid flow in an elongated passage bounded by dissimilar materials capableof setting up spontaneous potential differences in said liquid, comprising the steps of placing in they liquid insaid passage an exposed electrode adjacent to a permeable-insulatorcovered electrode, shielding both of said electrodes from spontaneous potentials due to the presence of the dissimilar materialsv bounding said passage and determining the potential 'dif-f ference between saidfelectr'odes.

3. Apparatus vfor locating the level in a well bore where fluid is entering or leaving said well bore comprising an electrically-conductive,r elongated housing adapted to be positioned in said well bore, cable means for raising and lowering said housing, passageway means through said housing, a pair of electrodes positioned within said passageway means, one of said electrodes being bare so that fluid flowing through said passageway may directly contact said electrode and the other of said electrodes vhaving a porous covering surrounding saidk electrode, and means for recording the potential difference between said electrodes in correlation to the depth of said apparatus in said well bore.

4. Apparatus for locating the elevation in a well bore where fluid is entering or leaving said well bore, comprising an electrically-conductive housing adapted to be positioned in said well bore, cable means for raising and lowering said housing, passageway means through said housing comprising an insulating sleeve extending substantially the length vof said electrically-conductive housing, a pair of electrodes mounted upon said sleeve at substantially the same elevation, one of the said electrodes being bare so that fluid flowing through said passageway means may directly contact said electrode and the other of said electrodes having a liquid-permeable covering surrounding said electrode, and means for recording the potential difference between said electrodes in correlation to the elevation of said apparatus in said well bore.

5. Apparatus for locating the level in a bore v hole where liquid is entering or leaving said bore hole comprising an electrically conductive, elongated cylinder adapted to be positioned in said bore hole. end members i'or said cylinder having ports therein to permit bore hole liquid to pass through said cylinder, cable means attached to one oisaid end members for raising and lowering said cylinder, an insulating sleeve positioned within said cylinder adapted to insulate the column of liquid passing through said cylinder from the natural potentials present within said bore hole, a pair of electrodes mounted within said sleeve, one of said electrodes being directly exposed to liquid ilowing through said sleeve and the other of said electrodes having a` porous, liquid-permeable casing surrounding said electrode, means insulating said electrodes from said cylinder and means for recording the potential difference between said electrodes in correlation to the depth of said apparatus in said well bore.

6. Apparatus in accordance with claim 5 in which said electrodes are constructed i'rom a metal selected from the group consisting of zinc, copper, brass and silver.

7. In combination, an electrically-conductive, elongated housing adapted to be positioned in a well bore, end members for said housing having port means therein to permit tree passageway of iluid into and out of said housing, cable means connected to one oi the said end members for raising and lowering said housing in a well bore, an insulating sleeve member extending substantially the length of said housing and defining an electrically-shielded passageway means through said housing, a pair oi electrodes constructed oi similar metals mounted within said sleeve at substantially the same distance along said passage- 'l way, one of said electrodes having a porous insulating coating wettable by the iluid to place said electrode in electrical contact with uid in said passageway means, ythe other of said electrodes being in physical contact with the fluid flowing in said passageway means, and means for s the addition of flexible cup means mounted exteriorly of said housing and adjacent an end thereof adapted to cooperate with the, side walls of said well bore.

9. The .method of locating the position in a l well bore where fluid is leaking through the wall of the well bore, which comprises the steps of positioning a pair of electrodes adjacent each other within'said well bore, one of said electrodes having its surface perviously covered to place l said electrode in electrical contact with said iiuid without exposure of said surface to iiuid movement and the other oi' said electrodes having its surface in contact with the moving uid, electrically shielding the fluid in the region of said electrodes from environmental potentials existing in said well bore, and measuring the potential ditference between said electrodes.

JOHN E. WALSTROM.

Menaces cnam the me of this pawns UNrrED s'rA'ras Psm'rs Number Name Date 1,913,293 scmumberger June e, 1933 2,184,338 Ennis Dec. 26, 1939 2,377,501 Kinley June 5, 1945 2,475,353 .I D011 July 5, 1949 2,475,354 D011 Julyv 5, 1949 2,517,603 Silverman Aug. 8, i950 '2,550,005 Doll Apr. 24, 195i OTHERREFERENCES 40 "The Review of Scientiiic Instru. October,"

1948, vol. 19, No. 10, pgs. S40-646. 

